1. Field of the Invention
This invention relates to an image forming apparatus wherein a moving image bearing member is cleaned by cleaning means held in contact therewith and wherein the cleaning means is also reciprocated in the longitudinal direction, i.e. transverse to the direction of movement of the image bearing member.
2. Description of the Prior Art
Image forming apparatus are known in which a sheet-like transfer material, such as paper, is brought into contact with the surface of an image bearing member on which a transferable toner image is formed. The toner image is transferred onto the transfer material in an electrostatic manner, and then the transfer material is separated from the image bearing member; and the above steps are repeated as necessary each time these steps are carried out it is required to remove the residual toner which has made no contribution to the transfer step and still remains on the surface of the image bearing member even after separation of the transfer material.
Therefore, various means for removing the residual toner have been proposed and put into practice. It is also well known to utilizer a plate-like cleaning blade made of an elastic material such as urethane rubber and having one edge, which is held in pressure contact with the image bearing member for scraping off the residual toner. This arrangement is simple in construction and small in size; and at the same time it provides excellent toner removing capability.
However, even such cleaning means is subject to several drawbacks. Firstly the toner accumulated at the edge portion may not fall and, after long use may become solidified and lift up the blade, thereby reducing its cleaning capability. Secondly the accumulated toner may deposit and fuse onto the image bearing member, and thereby degrade the image quality.
As means for removing deposits on the photoreceptor surface, it is also known to provide an elastic roller or the like comprising a sponge layer and an elastic rubber material coated thereon. The elastic roller is particularly effective in removing the products attendant on corona discharge produced at chargers, paper dust, etc. which, in conditions of high humidity may cause the image to run. However, since the elastic roller is moved to slide on the photoreceptor surface while maintaining highly pressurized contact therewith, scratches in the form of streaks are in the circumferential direction of the photoreceptor, and hence undesired streaks emerge, thereby degrading the image quality.
To avoid the foregoing drawbacks, it is also proposed to reciprocate the cleaning blade or elastic roller in the longitudinal direction thereof with an appropriate stroke. With this technique, a kind of stimulus is given to the toner particles for preventing the toner from being accumulated and also preventing foreign matter from being deposited. In case of using the elastic roller, the above technique is likewise effective in preventing the streak scratches in the circumferential direction of the photoreceptor. For example, Japanese Patent Laid-Open No. 62-105181(1987) discloses one type of cleaning blade which is reciprocated in the longitudinal direction of the image bearing member.
However, when the cleaning blade or the elastic roller is reciprocated, the photoreceptor and other components necessarily are more susceptible to vibrations particularly at the time of turning in the direction of movement, which may result in degraded image quality due to blurs or the like. Above all, in the case of laser printers, digital reproduction machines, and digital color reproduction machines, where a minute spot of laser beam is scanned on the photoreceptor surface for forming a latent image, spot positions are often so drifted that the latent image is disordered and the image quality is degraded. Especially, in full color reproduction machines, where development of respective colors is carried out onto a photoreceptor several times, and a toner image in each color is repeatedly transferred onto a transfer material held on a transfer material bearing member (hereinafter referred to as a transfer drum), vibrations due to reciprocal movement of the cleaning blade or elastic roller cause transfer shifts, resulting in the degraded image quality.